The present invention is an improvement in the type of filtration system disclosed in U.S. Pat. No. 4,242,205. The traveling belt type of filter therein disclosed has been used for filtration of liquid such as coolants utilized in machining operations. The filter media may be of the permanent type, comprising a mesh polymeric mono-filament material, which is cleaned at the point of dirt discharge by air blow-off and/or washer headers. Alternatively, the media may be expendable cellulosic and/or polymeric material.
In the intermittent traveling belt type of filter, commonly used for coolant filtration, the build-up of sludge forms a filter cake which itself acts as a fine filter to capture contaminants as the liquid penetrates the depth of the filter cake. The accumulation of this filter cake produces an increase in resistance to liquid flow through the filter cake and media, resulting in a pressure differential which can be sensed and utilized to automatically interrupt the filtration process to permit the media to be indexed to bring clean media into registry with the openings in the submerged filter box.
In this type of construction, the effectiveness of the seal between the longitudinal edge of the filter media and the surface of the filter box is an important contributing factor to the efficiency of filtration. The increased resistance to flow through the filter cake and media resulting from the accumulation of contaminants increases the likelihood of contaminated liquid by-passing the edges of the filter media through any available leakage paths.
The prevention of leakage along the longitudinal edges of the filter belt has been a problem confronting the workers in the filtration art. Fabric filter belts are subjected to alternating exposure to liquid and air, causing shrinkage, which problem has been generally compensated for by utilizing an initially over-sized belt. Fabric belts are also subject to wrinkling. The low specific weight of these fabrics requires means for forcibly holding the fabric edges against the periphery of the filter box, to prevent the undesired by-pass leakage. The transverse angle flights which span the filter belt between the driving chains to assist in conveying away accumulated sludge are generally spaced at about two foot intervals, and therefore do not provide effective sealing pressure along the longitudinal edges of the belts. Stationary seals, relying upon engagement with the intermittently moving belt, are subject to wear and may tear the fabric belt. Resilient seals traveling with the belt are impractical because such seals would have to traverse the same drive sprockets or drums which the filter belt loops traverses.
The above-referred to U.S. Pat. No. 4,242,205 discloses a supplementary chain located laterally adjacent the inside edge of the driving chain and moving therewith, which chain functions solely to hold down, by gravity, the filter belt edges against the filter box. Where an additional opening is provided in the lower surface of the box to increase the effective filtration area, gravity is not available to provide sealing pressure to hold the chain against the lower reach of the belt and the filter box. Therefore, it is necessary to utilize a supplementary system of compression springs and tracks to engage the lower reach of the chain and bias it upwardly against the lower reach of the filter belt loop.
It is the principal object of the present invention to provide an improved sealing system to prevent leakage of contaminated liquid around the longitudinal edges of a filter belt, and particularly, a system which also lends itself to effectively seaing the lower reach of the filter belt against the bottom face of the filter box.